Improve expected types for dependent functions

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1146,12 +1146,15 @@ class Typer extends Namer
           // if expected result type is a wildcard, approximate from above.
           // this can type the greatest set of admissible closures.
           (pt1.argTypesLo.init, typeTree(interpolateWildcards(pt1.argTypesHi.last)))
-        case SAMType(sam @ MethodTpe(_, formals, restpe)) =>
+        case RefinedType(parent, nme.apply, mt @ MethodTpe(_, formals, restpe))
+        if defn.isNonRefinedFunction(parent) && formals.length == defaultArity =>
+          (formals, untpd.DependentTypeTree(syms => restpe.substParams(mt, syms.map(_.termRef))))
+        case SAMType(mt @ MethodTpe(_, formals, restpe)) =>
           (formals,
-            if sam.isResultDependent then
-              untpd.DependentTypeTree(syms => restpe.substParams(sam, syms.map(_.termRef)))
-            else
-              typeTree(restpe))
+           if (mt.isResultDependent)
+             untpd.DependentTypeTree(syms => restpe.substParams(mt, syms.map(_.termRef)))
+           else
+             typeTree(restpe))
         case _ =>
           (List.tabulate(defaultArity)(alwaysWildcardType), untpd.TypeTree())
       }